Loud-speaker enclosure



May 12, 1964 MADDY 3,132,712

LOUD-SPEAKER ENCLOSURE Filed Jan. 4, 1960 RP PS INVENTOR. W/YbUr L.Maddy Z: T 4 ATTORNE rs.

electrical signals. have resulted in more and more expensive, complexand space-consuming apparatuses. many skilled in the high fidelity soundfield that satis- United States Patent M 3,132,712 LOUD-SPEAKERENCLOSURE Wilbur L. Maddy, 2051 Central Park, Apt. 2,

Topeka, Kans. Filed Jan. 4, 1960, Ser. No. 212 4 Claims. (Cl. 181-31)This invention relates generally to the field of sound transducerequipment and, more particularly, to improvements in enclosureapparatusfor loud-speakers such as are utilized for the reproduction of music,speechor other audio intelligence in homes, stores and othersurroundings.

The increasing interest in recent years in the high fidelityreproduction of sound has focused attention upon the sound reproducingportion of high fidelity systems, since it has been recognized that,regardless of the degree of perfection attained in the handling of audiofrequency electrical signals, the final usable output, that is, thereproduced sound itself, is limited in its quality by the operation ofthe sound transducing portion of the system. The prior art has soughtmany solutions to the problem of attaining high quality soundreproduction of audio In the main, however, these efiorts It iscurrently felt by believed that such large speaker mustbe supplementedby one or more additional loud-speakers or tweeters to handle certainhigher frequency parts of the range of sounds to be reproduced. Morerecently, the problem has been further compounded by the necessity ofproviding a pair mental to the obtaining and enjoyment of high qualitysysterms by the average householder.

Accordingly, it is the primary object of this invention to provide soundreproducing apparatus of an improved type adapted to give qualityreproduction performance at moderate cost and with a minimum ofcomplexity and consumption of space.

It has been found that loud-speakers of even the smaller sizes, such aseight inch cone diameter will, without supplementation by additionalspeakers or tweeters, give extremely realistic and pleasing soundreproduction per formance when enclosed by means such as contemplated bythe present invention, which advantageously is also relatively small insize and inexpensive to manufacture.

It is, therefore, a further object of the invention to provide enclosureapparatus for use with conventional loud-speakers of any size, butparticularly adapted for improving the overall performance which may beobtained from loud-speakers of the smaller sizes now seldom consideredeven usable for overall frequency reproduction in high fidelity systems.

It is a further important object of the invention to provide suchenclosure apparatus which will be of greatly decreased volume, ascompared with any of the nowconventional types of high fidelityloud-speaker enclosures.

It is a further object of the invention to provide such enclosureapparatus which may be constructed of various .materials including,preferably, a wooden cabinet, but

also including cabinet structures of metal, plastic or the like, withoutthe disadvantageous effects of vibrations,

resonances and the like which are suffered in conventional 3,132,712Patented May 12, 1964 ice types of speaker enclosure apparatuses whenmaterials of the latter types are employed.

Itis another of thevery important objects of the invention to provideand utilize in association with the cabinet structure of the enclosure,an improved type of acoustical filter disposed within the cabinetstructure in such relation to the latter and to the rear of the cone ofthe loudspeaker as to automatically adapt to the dynamiodiaphragm actionof the speaker cone and the levels of fre quency and amplitude of soundsbeing transduced in such manner as to improve the reproduction qualitieswhich would otherwise be enjoyed from the speaker employed to such anextent .that an eight inch speaker of moderate cost, for example, willgive results comparable to, if not better than, loud-speakers ofalmosttwice that size and several times that cost housed in ordinaryenclosures.

It is another object of the invention to provide such enclosureapparatus for loud-speakers, which. is dimerisioned in accordancewithcertain critical ranges of proportions of the various dimensions, whichcooperate with the improved acoustical filteremployed in the apparatusof the invention, in such manner that sound waves in duced in the airwithin the cabinet structure rearwardly of the cone of the loud-speakerby the dynamic diaphragm action of the latter, will be damped inamplitude and re tarded during both their rearward emanation from thespeaker cone. and their forward reflection back to the latter by thecabinet structure in a manner affected by the frequency and amplitude ofthe particular sound waves being handled, so thatthe reflected rearwaves are controlled to supplement by positive acoustical feedback ofcritically proper amount and phase the electrically induced originalaction of the speaker cone in producing a high quality andfaithful'reproduction of the audioelectrical signals fed to theloud-speaker.

,for construction out of materials having hard Walls, its

adaptability for construction in attractive nonsymmetrically shapedcabinets and other features and details of side edge of a loud-speakerenclosure apparatus constructed in accordance with the invention;

FIG. 2 is a cross-sectional view of the apparatus of FIG. 1, takenlooking rearwardly from immediately to the rear of the front-wall of theenclosure structure; as

illustrated by the line 22 of FIG. 3, the loud-speaker being removed toshow the interior of the enclosure structure; and

FIG. 3 is a cross-sectional view of the apparatus of FIG. 1, takenlooking downwardly from immediately be low the top wall of the enclosurestructure, as illustrated by the line 3-3 in FIG. 2. q

It should be pointed out at the outset, that the natural qualities ofsound reproduction, the sound propagation characteristics and theoverall fidelity and performance which have been achieved by utilizingconventional loudspeakers of moderate size and conventional design inthe 70.

improvedenclosure apparatus of this invention, have been of suchsurprising excellence, as compared either with the same loud-speakerenclosed in conventional enclosures or with even much larger and moreexpensive conventional or specially designed loud-speakers in large,expensive conventional enclosures of various types, that it is difficultto fully explain on a theoretical basis exactly why such startlinglyimproved results are achieved by the invention. Accordingly, at thistime, no detailed theoretical explanation of the advantageous phenomenaachieved will be attempted. However, current observations indicate thatthe performance characteristics of the invention mentioned probablydepend upon certain critical ranges of the proportioning of thedimensions of the cabinet structure of the enclosure and/or the natureof the acoustical 'filter employed and its relationship to the cone ofthe loud-speaker and the inner surfaces of the walls of the cabinetstructure.

wall 12 and generally parallel to the latter, and a top wall 16, abottom wall 18 and a pair of side walls 20 and 22 extending between thefront and rear walls 12 and 14 respectively and presenting a cabinetstructure which is completely enclosed except for an opening 24 providedin the front wall 12. The walls 12, 14, 16, 18, 2t) and 22 may besecured together in any suitable fashion and,

when the cabinet structure is formed of metal, plastic or the like, mayinclude integral connections between certain of the walls. Where thecabinet structure of the apparatus lil is constructed of wood, any ofthe techniques known to the Wood cabinetry art, such as glue, screws orthe like, will be satisfactory for assembling the walls tov gether, theimportant thing being that the cabinet structure is relatively rigid andrelatively airtight, except for the opening 24.

With constructions of the cabine structure from other materials, meansfor the interconnection of the wall elements may be taken from thosewhich are conventional and known by persons skilled in the art ofconstructing objects from such materials.

The cabinet structure presented by the walls 12, 14, 16, 18, 20 and 22present a housing for enclosing and mounting a loud-speaker generallydesignated 26 whose frame 28 may be secured to the front wall by anyconventional fastening means such as at 30. The speaker 26 also includesa magnet or coil portion as at 32 adapted for electrical connection witha source of audio frequency electrical signals and a cone 34 adapted tobe vibrated by the action of such electrical signals upon the magnet orcoil portion 32. It is to be understood that such speaker 26 may be ofconventional design and could be, for example, either of the permanentmagnet or dynamic type. The important consideration, or more accurately,privilege conceded by the invention in connection with the loud-speaker26, is that it may be of relatively small size both in terms of thediameter of the cone 34 and the overall depth of the speaker assembly26. Shallow loud-speakers of eight inch diameter have been found toproduce superb results when utilized with the enclosure apparatus ofthis invention. The speaker 26 should be so positioned on the front wall12 that the cone 34 aligns with the opening 24 in the front wall 12, itbeing understood that such opening 24 will be of size generallycorresponding to the effective diameter of the cone 34. In order toprotect the speaker cone 34 from the entry of foreign materials throughthe opening 24, as well as to improve the decorative qualities of theapparatus 10, a porous grill cloth as at 36 may be extended over theopening 24 and, if desired for decorative purposes, also extended over aportion or all of the front wall 12 and suitably fastened in anyconventional manner, the illustrative embodiment being described showingthe fastening of the grill cloth 36 by the sandwiching of oppositemargins thereof between the front wall and the corresponding side wall20 or 22 as at 38.

The acoustical filter forming an important part of the inventivestructure is generally designated by the numeral 40. Such filter 40 ispreferably formed from a generally rectangular piece of materialcommonly known as rubberized horsehair padding material, which finds itsheretofore usual application in the field of upholstering. Suchmaterial, which is used for the acoustical filter 40 in the preferredillustrative embodiment of the invention, is formed of a great number ofrandom disposed, relatively stiff horsehair fibers which areindividually coated, in

whole 'or in part, by a rubber or other elastic material, which alsoserves to interconnect the random disposed fibers at their zones ofmutual contact. The material mentioned is available in sheets of variousthicknesses from about one inch to about two inches in thickness. Forenclosure apparatus 10, for accomodating an average size eight inchloud-speaker, the acoustical filter 40 may be preferably of about oneand one-half inches thickness, while for the shallower size speakers ofeight inch diameter or for larger speakers, a thickness of about twoinches for the acoustical filter 40 is to be preferred.

The "acoustical filter 40 is bent forwardly on each side of a centralportion 43 thereof, preferably into the generally arcuate configurationof a wall section of a cylinder and is disposed within the cabinetstructure of the apparatus 10 so that a rearwardly convex centralportion of the filter 40 is disposed along and in contact with anelongated central portion of the rear wall 14 as at 42. The oppositefront surface of the acoustical filter 40 preferably extends forwardlyinto contact with the rear of the magnet or coil portion 32 of thespeaker 26 as at 44. The opposite side portions 46 and 48 of theacoustical filter 40 then bend arcuately forwardly and to the side andeach extend into contact. with the inner surface of the cabinetstructure in proximity to the corresponding of the inner corners 50 and52 presented by the juncture of the side walls 20 and 22 respectivelywith the front Wall 12.

'The acoustical filter 40 thus divides the hollow interior of thecabinet structure of apparatus 10 into a chamber 54 forwardly of thefilter 4t and in which the speaker 26 is received, and a pair of rearchambers 56 and 58 between the rear of the filter 4t and the rear wall14 on the opposite sides of the area of interengagement as at 42. Thedegree of arcuate bending of the filter 40 is, of course, controlled bythe general proportions of the interior of the cabinet structure of theapparatus 10.

It has been found that the dimensioning of the walls 12 et seq. of thecabinet structure of apparatus v10, involve critical ranges ofproportions, if the unexpectedly desirable results of the invention areto be fully achieved, which may be defined as including constructions inwhich the lateral dimension of the front wall 12 and side wall 14running generally parallel to the elongated area of contact 42 betweenthe filter 40 and the rear wall .14, is between about one hundredpercent and one hundred twenty-five percent of the other orperpendicular, lateral dimension of such front wall 12 and rear wall 14running perpendicularly to the elongated area ofcontact 42 and in whichthe dimension of the side walls 20 and 22 and the top walls 16 and 18perpendicular to the aforesaid lateral dimensions of said front wall 12and rear wall 14, i.e., the distance between front wall 12 and rear wall14, is between about thirty percent and about fifty percent of thelast-mentioned lateral dimension of the front wall 12 and rear wall 14.It may be observed that the enclosure apparatus 10 functionsequally Wellwhether disposed or oriented as illustrated in the drawing or turnedupon its side; accordingly, the dimensions in question have thus beenreferred to as perpendicular lateral dimensions of the front and rearwalls 12 and 14 rather than height and width, which may be interchangedby different disposition of the apparatus 10. Satisfactory functioningof the apparatus has been achieved with various sizes of cabinetstructures, and, of course, correspondingly dimensioned filters 40, whenthe proportions thereof have been chosen with-in the ranges justmentioned. It has been further observed, however, that a slight peakingor optimization of even such vastly improved results is enjoyed when thelength, width and front to back depth of the cabinet structure areapproximately in the ratio of 100:80z30 respectively, where the lengthis defined as the dimension generally parallel to the area of engagement42 and width is defined as the dimension generally perpendicular to sucharea of engagement 42. One example of dimensioning of the cabinetstructure of the apparatus which has been found very satisfactory inoperation and capable of attaining the markedly improved resultscharacterizing the invention, involved a height of sixteen and one-halfinches, a width of twelve and one-half inches, and a depth of four andone-half inches where a conventional eight inch loudspeaker 26 wasemployed. Another illustrative example of dimensioning found to besatisfactory with a twelve inch loud-speaker was a height of eighteenand one-half inches, 21 width of fourteen and one-half inches and depthof six and one-half inches. It should be noted that all of thereferences to dimension and proportions thereof of the cabinet structureof enclosure apparatus 10 mentioned hereinabove and in the claims thatfollow, refer to theinner dimensions of the Walls 12, 14, 15, 18, 20 and22 which define the chamber within the enclosure structure 10.

Having thus described an illustrative, preferred embodiment of theinvention, the principles and concepts involved will be clear. Itnecessarily follows that those skilled in the art may make a number ofminor variations, modifications or adaptations of the apparatusdiffering in specific constructional detail from the preferredembodiment described without departing from the true spirit, principlesand teachings of the invention. Accordingly, it is to be understood thatthe invention should be deemed as limited only by the scope of theclaims that follow.

Having thus described the invention, what is claimed as new and desiredto be secured by Letters Patent is:

1. Enclosure apparatus for a loud-speaker of the type provided with anopen frame, an assembly on said frame for converting audio frequencyelectrical signals applied to said assembly into audio frequencymechanical vibrations of a part of said assembly, and a speakerdiaphragm structtue having an outer portion thereof supported on saidframe, an inner portion thereof coupled with said part for vibrationwith the latter and both generally forwardly facing and generallyrearwardly facing areas thereof exposed, said apparatus comprising ahousing having a front Wall provided with an aperture therein and wallmeans interconnecting said front wall to present a closed chamber Withinsaid housing except for said aperture, said Wall means comprising asound rellecting rear wall in spaced relationship to said front wall andsound refleeting side wall means interconnecting said front and rearWalls; means for mounting said frame of said loudspeaker on said housingto dispose said diaphragm structure within said chamber and in alignmentwith said aperture; and an acoustical filter having negligible dampingand absorption effects on sound Waves propagated theret'hrough, saidfilter comprising a fibrous, sound pervious partition having a generallyconcave side and an opposite, generally convex side, said partitionbeing of substantially uniform thickness and composed of randomdisposed, relatively stiff fibers at least partially coated andinterconnected at zones of contact therebetween by a resilient bindersubstance, the partition being disposed within said chamber between saiddiaphragm structure and said rear wall and extending generallylater-ally of said chamber with a central portion of said generallyconvex side engaged with said rear wall and the opposite, generallyconcave side of said portion engaged with said assembly.

2. Apparatus as set forth in claim 1, wherein said chamber isparallelepipedal and characterized by a dimensional relationship inwhich one lateral dimension thereof is between about 100% and about 125%of the other lateral dimension thereof, and the front-to-back dimensionthereof is between about 30% and about of said other lateral dimensionthereof.

3. Apparatus as set forth in claim 2, wherein said chamber ischaracterized by a dimensional relationship in which its length, widthand front-.to-back depth are in the approximate ratio of :80:30respectively.

4. Apparatus as set forth in claim 1, wherein said partition is composedof rubberized horsehair padding material.

References Cited in the file of this patent UNITED STATES PATENTS1,844,802 Seabert Feb. 9, 1932 2,065,751 Scheldorf Dec. 29, 19362,775,309 Villchur Dec. 25, 1956 3,082,839 Whitcas Mar. 26, 1963 FOREIGNPATENTS 434,563 Great Britain Sept. 4, 1935 483,745 Great Britain Apr.26, 1938 512,610 Great Britain Sept. 21, 1939 1,005,731 France Jan. 2,1952 502,238 Italy Nov. 29, 1954 1,154,792 France Nov. 12, 1957

1. ENCLOSURE APPARATUS FOR A LOUD-SPEAKER OF THE TYPE PROVIDED WITH ANOPEN FRAME, AN ASSEMBLY ON SAID FRAME FOR CONVERTING AUDIO FREQUENCYELECTRICAL SIGNALS APPLIED TO SAID ASSEMBLY INTO AUDIO FREQUENCYMECHANICAL VIBRATIONS OF A PART OF SAID ASSEMBLY, AND A SPEAKERDIAPHRAGM STRUCTURE HAVING AN OUTER PORTION THEREOF SUPPORTED ON SAIDFRAME, AN INNER PORTION THEREOF COUPLED WITH SAID PART FOR VIBRATIONWITH THE LATTER AND BOTH GENERALLY FORWARDLY FACING AND GENERALLYREARWARDLY FACING AREAS THEREOF EXPOSED, SAID APPARATUS COMPRISING AHOUSING HAVING A FRONT WALL PROVIDED WITH AN APERTURE THEREIN AND WALLMEANS INTERCONNECTING SAID FRONT WALL TO PRESENT A CLOSED CHAMBER WITHINSAID HOUSING EXCEPT FOR SAID APERTURE, SAID WALL MEANS COMPRISING ASOUND REFLECTING REAR WALL IN SPACED RELATIONSHIP TO SAID FRONT WALL ANDSOUND REFLECTING SIDE WALL MEANS INTERCONNECTING SAID FRONT AND REARWALLS; MEANS FOR MOUNTING SAID FRAME OF SAID LOUDSPEAKER ON SAID HOUSINGTO DISPOSE SAID DIAPHRAGM STRUCTURE WITHIN SAID CHAMBER AND IN ALIGNMENTWITH SAID APERTURE; AN ACOUSTICAL FILTER HAVING NEGLIGIBLE DAMPING ANDABSORPTION EFFECTS ON SOUND WAVES PROPAGATED THERETHROUGH, SAID FILTERCOMPRISING A FIBROUS, SOUND PERVIOUS PARTITION HAVING A GENERALLYCONCAVE SIDE AND AN OPPOSITE, GENERALLY CONVEX SIDE, SAID PARTITIONBEING OF SUBSTANTIALLY UNIFORM THICKNESS AND COMPOSED OF RANDOMDISPOSED, RELATIVELY STIFF FIBERS AT LEAST PARTIALLY COATED ANDINTERCONNECTED AT ZONES OF CONTACT THEREBETWEEN BY A RESILIENT BINDERSUBSTANCE, THE PARTITION BEING DISPOSED WITHIN SAID CHAMBER BETWEEN SAIDDIAPHRAGM STRUCTURE AND SAID REAR WALL AND EXTENDING GENERALLY LATERALLYOF SAID CHAMBER WITH A CENTRAL PORTION OF SAID GENERALLY CONVEX SIDEENGAGED WITH SAID REAR WALL AND THE OPPOSITE, GENERALLY CONCAVE SIDE OFSAID PORTION ENGAGED WITH SAID ASSEMBLY.